''Quasidirect'' observations of cosmic-ray primaries in the energy region 10/sup 12/--10/sup 14/ eV

We have exposed an emulsion chamber at a level of 32.8 g/cm/sup 2/ for /similar to/30 h, and detected /similar to/800 showers on x-ray films (Fuji No. 200 type). Among these, /similar to/200 primaries(/Sigma/ /ital E//sub /gamma///ge/2TeV, /theta//lt/75/degree/) were identified by tracing back through successive plates of nuclear emulsion. On the basis of these primaries, we obtain /ital I//sub /ital p//(/ge/E/sub 0/)=1.02/times/10/sup /minus/5/ (/ital E//sub 0//(1 TeV))/sup /minus/1.82/plus minus/0.13/ (cm/sup 2/ sec sr)/sup /minus/1/ in the region 5/approx lt//ital E//sub 0//approx lt/100 TeV for proton primaries, and /ital I//sub /alpha//(/ge/E/sub 0/) =6.50/times/10/sup /minus/7/(/ital E//sub 0//(1 TeV/nucleon))/sup /minus/1.75/plus minus/0.15/ (cm/sup 2/ sec sr)/sup /minus/1/ in the region 3/approx lt//ital E//sub 0//approx lt/10 TeV/nucleon for /alpha/ primaries. We observed also many atmospheric secondary /gamma/ rays, which cover the energy region 2--80 TeV. The /gamma/-ray spectrum is a rather smooth continuation of that obtained by Nishimura /ital et al./ in the region 0.2--2 TeV. The higher-energy part of our flux, however, cannot be reproduced by the atmospheric nuclear interaction of the primary protons and /alpha/ particles alone, indicating that, for energies /approx gt/10/sup 14/ eV/nucleus, the contribution of heavier primaries becomes significant, and that the latter flux may very well become comparable withmore » the proton flux somewhere between 10/sup 14/ and 10/sup 15/ eV/nucleus. This indication is consistent with the iron flux obtained directly by the present experiment, though poor statistics preclude a conclusive result.« less